Knee implants: more evidence needed?

The effectiveness of knee replacement surgery was in the news today, when the BBC and Independent reported that more evidence was needed on the long-term safety of knee implants.

The news, which follows recent reports on the safety of PIP breast implants and certain metal hip implants, is based on a report on knee replacement surgery published in The Lancet medical journal. It argued that although knee replacement surgery is highly successful as a treatment for osteoarthritis, there is a need for more long-term monitoring of surgery outcomes and steps to ensure that patients selected for surgery are suitable.

In addition, the report’s authors say that new implant designs are continually being introduced, often with little or no evidence of their effectiveness, and that more long-term monitoring of their safety and effectiveness is needed.

Although some online news sources have suggested that the review article found knee replacement to be dangerous, this is misleading. The report says that knee replacement is generally successful but that more needs to be done in assessing which patients will benefit, in collecting data on outcomes and in carefully monitoring the introduction of new implant designs.

Knee replacements are usually carried out when the knee has been damaged by arthritis. In most cases, surgery is for osteoarthritis, the most common form of this disease, although it is also used for other forms. In osteoarthritis, the parts of the knee that slide over each other as you move become damaged, through either gradual wear or an injury. Only a small number of people with arthritis in the knees are given knee replacement surgery. It is usually considered if someone is in persistent, disabling pain and if non-surgical treatments, such as physiotherapy, have not helped.

During the operation, the surfaces of the knee joint that have been damaged by arthritis are removed and replaced by new parts, made of metal and plastic. In effect, this artificial hinge replicates the natural range of movements of the knee. Patients can have either a total knee replacement (TKR), in which all the surfaces are replaced, or a partial knee replacement, in which only part of the knee is replaced. A TKR is the most common form of the operation.

Knee replacement surgery is an increasingly common procedure and the number of operations is rising annually. Over 70,000 knee replacement operations are carried out each year, about four out of five of them in women. In the UK, rates of knee replacement operations in women increased from 43 per 100,000 person years in 1991 to 137 per 100,000 person years in 2006.

The average age for having this surgery is 70 years old but, according to the new report, knee replacement is increasingly being considered for patients younger than 55. The authors say that the reason for this trend is unclear. For example, it could be due to increased patient expectation or more osteoarthritis among young people because of the increasing incidence of obesity.

Knee replacement surgery is generally considered to be a highly successful operation. It improves pain, mobility and quality of life in many people with advanced arthritis of the knee joint. The charity Arthritis Research says that about four out of five people who’ve had the operation say they are happy with their new knees. However, some people are disappointed with the outcome of their surgery or are unsure whether there has been an improvement.

This is why it’s important to ensure that patients considered for the operation are those who would derive the most benefit. The National Institute for Health and Clinical Excellence (NICE) says that although joint replacement operations can provide very good pain relief for many people with osteoarthritis, in a substantial number of cases the outcome is not good enough. “It would be very useful to have pre-operative tools to help choose the people who would derive most benefit,” NICE commented.

The new review article argues that there’s an urgent need for improved decision making to assess whether a patient should undergo the procedure. Evidence-based information should be given to patients about factors that are known to influence the outcome of their surgery.

The article also says that long-term monitoring of outcomes is needed, through national joint-replacement registries and electronic patient records reporting the rates of revision surgery and other outcomes.

All major operations carry some immediate risks, including blood clots and infection. In the longer term, knee replacement surgery can lead to complications. These include the knee giving way (instability) or continuing to hurt, numbness around the joint, problems with bending and the need for a second operation to correct or remove part of the implant, known as revision surgery. The need for revision surgery is often the result of the new joint becoming loose. Other common reasons include infection, pain and stiffness.

Some internet news reports implied that the review has judged knee replacements to be unsafe. However, the article primarily discussed the decision-making processes behind knee replacement surgery and the need to gather evidence on the best practice for knee replacement and on the effectiveness of new implant designs. It did not suggest that knee replacement is unsafe or that it should be stopped, although it did argue for improved collection of safety data.

The report says that orthopaedic manufacturers are continually introducing new designs for implants and that doctors expect that these new implants will improve outcomes. However, there is evidence to suggest “this belief is incorrect.” The new implants are often introduced with little or no evidence of their effectiveness, it adds.

Limited release of new implant designs as part of well-conducted large-scale randomised controlled trials is essential, the authors argue. In addition, national joint registries should monitor the outcomes of new implant designs.

The report says that national joint replacement registries, such as the UK’s National Joint Registry (NJR), are one of the best and most important sources of data on knee replacement surgery. These registries collect data on measures such as revision surgery, as well as patient-reported outcomes.

According to the report, improved long-term monitoring of outcomes using both national registries and electronic patient records should be undertaken. This is so that both patients and surgeons have good-quality evidence to assess different implants and techniques and to improve decision making.

The Medicines and Healthcare products Regulatory Agency has reportedly said that since April 2003, all knee joint replacement operations in England and Wales have been recorded by the NJR.

If your implant is causing problems or you are anxious about it, ask your GP to refer you to your surgeon.